The present invention relates to a method and apparatus for radiography and to a gaseous avalanche detector.
X-rays have been used in radiographic imaging for a long time, and have been subject to great developments. In its simplest form, imaging is conducted by providing a source of X-ray radiation, an object to be imaged, through which the radiation is transmitted, and a detector for the detection and recording of the transmitted radiation. X-rays may also be scattered by the object to be imaged and detected by the detector. The X-ray detector used today, at hospitals, is normally a screen-film combination. In a phosphor screen (e.g. Gd2O2S), X-ray photons are converted and thereby produce secondary light, which is registered on a photographic film. The use of a film limits the dynamic range of the image. The increased efficiency achieved by using a phosphor screen is provided at the expense of resolution, since the secondary light is emitted isotropically.
Digital X-ray detectors today are normally made of some type of semiconductor detector, e.g. CCD, TFT, etc. To cover the large image format necessary in most medical X-ray imaging the detectors have to be made large, which in most cases results in a high production cost and low yield. One way to solve this problem is to make the detector modular and tiled together to form a large image format.
However the use of such an assembly of semiconductor X-ray detectors introduces a further problem in that blind, non radiation-detecting areas are introduced at the borders of the individual detectors, since semiconductor detectors needs a so called guard ring around them to limit the leakage current.
A solution to this problem is disclosed in U.S. Pat. No. 5,381,014 wherein they fabricate a large area X-ray image capture element by juxtaposing a plurality of discrete array modules in an assembly over a base plate so that each module is adjacent to at least one other module to form a two-dimensional mosaic of the modules. Each module includes a plurality of thin film transistors (TFT) arrayed adjacent on the top surface of a dielectric substrate and at least one precision ground edge of the substrate forms a precise abutment with a one precision ground edge of another substrate. A continuous radiation detecting layer is then disposed over the plurality of juxtaposed modules to form the large format element which minimises non-radiation-detecting areas between modules.
A drawback with this prior art is that each module of the detector has to be in physical and electrical contact with each other in order to produce said large area X-ray image capture element which will result in a relatively high manufacturing and assembling cost.
Another drawback with this type of modular detector is that the data and address circuits from each module have to be connected to the corresponding circuits in the neighbouring modules which will also result in a relatively high assembling cost.
Yet another drawback with this type of modular detector is that a broken module cannot be replaced without having to remove and redeposit the radiation detecting layer, if at all possible.
It is an object of the present invention to provide an X-ray detector and a method and apparatus for radiography that at least reduces the above mentioned drawbacks.
According to an aspect of the present invention, there is provided a method for obtaining images in radiography, comprising
emitting X-rays from an X-ray source,
detecting the X-rays which have been interfered by an object to be imaged in a gaseous avalanche detector including electrode arrangements between which a voltage is applied for creating an electrical field, and
detecting electrical signals in at least two detector electrode modules, said electrical signals being induced by electron-ion avalanches, in at least one of a plurality of detector electrode elements arranged adjacent to each other, each along a direction essentially parallel to the incident radiation, and where the at least two independent detector electrode modules are arranged, each along a direction essentially parallel to the incident radiation, and an apparatus for use in radiography, comprising
an X-ray source,
a gaseous avalanche detector, including electrode arrangements between which a voltage is applied for creating an electrical field, for detecting X-ray photons which have been interfered by an object to be imaged,
at least two independent detector electrode modules including a plurality of detector electrode elements arranged adjacent to each other, each along a direction essentially parallel to the incident radiation, and
where said at least two independent detector electrode modules are arranged along a direction essentially parallel to the incident radiation.
respectively and a gaseous avalanche detector for detecting incident radiation, including electrode arrangements between which a voltage is applied for creating an electrical field, wherein
the gaseous avalanche detector comprises a gaseous avalanche chamber for detecting incident radiation, and
at least two independent detector electrode modules including a plurality of detector electrode elements arranged adjacent to each other, each along a direction essentially parallel to the incident radiation, and
where said at least two independent detector electrode modules are arranged along a direction essentially parallel to the incident radiation.
Further objects are attained by further features in the appended claims.
An advantage of having at least two detector electrode modules is that they provide independent modules and therefore are easy to exchange.
Another advantage of having independent modules is that they neither need to be in physical nor in electrical contact with each other which simplifies the ability to change said arrangements, and reduces the assembly cost.
Yet another advantage of having independent modules according to the present invention is that the mechanical tolerances of each module are less severe compared to modules in a semiconductor detector and hence the manufacturing cost is reduced.
Still another advantage of having at least two detector electrode modules is that the detector will be less expensive per area unit compared to single large detector area.
Still another advantage of having at least two detector electrode modules is that the yield of the assembled detector will be higher compared to a single large detector area.
Still another advantage is that the requirements of the materials of substrate on which the conducting electrodes are arranged is not critical since said substrate is only used as a carrier for said conducting elements and therefore the manufacturing cost is reduced and the production yield is increased.
Still another advantage with the inventive modular detector is that the detector electrode modules do not need to be deposited by a radiation detecting layer which simplifies manufacturing, assembly and replacement of said modules.